The present invention relates to magnetic disc drive data storage devices and, more particularly, to a method of reducing or eliminating asperities on a disc surface.
In disc drive data storage devices, digital data are written to and read from a thin layer of magnetizable material on a surface of one or more rotating discs. Write and read operations are performed through a transducer which is carried in a slider body. The slider and transducer are sometimes collectively referred to as a head, and typically a single head is associated with each disc surface. The heads are selectively moved under the control of electronic circuitry to any one of a plurality of circular, concentric data tracks on the disc surface by an actuator device. Each slider body includes an air bearing surface (ABS). As the disc rotates, the disc drags air beneath the ABS, which develops a lifting force that causes the head to lift and fly several microinches above the disc surface.
In operation, the magnetic head can come into contact with asperities on the surface of the disc while the head flies above the surface of the disc. Potentially, this undesirable contact can cause data written to a particular location on the disc to be lost. Immediately after contact with an asperity, the heat generated by the contact changes the resistive properties of the magnetoresistive (MR) head. As a result, the corresponding signal read by the MR head is distorted by a voltage spike and subsequent decay, sometimes causing the data stored near the asperity to be unrecoverable. The voltage spike in the read signal is frequently referred to as a "thermal asperity," while the feature on the disc is referred to as an "asperity". However, since one is indicative of the other, the two terms are frequently used interchangeably.
Disc asperities which are located in the factory during the defect scanning process can be recorded in the disc drive's primary defect list, so that the drive does not store data at those locations. However, it is preferable to reduce the number of asperities on the surface of the disc in order to maximize available storage space and to minimize head-to-asperity contact during operation. Consequently, an improved method of reducing the size and/or number of asperities on the surface of the disc would be a significant development in the field.